This invention relates to the beneficiation of shredded metal scrap material. More particularly, it is concerned with the beneficiation of shredded aluminous scrap materials, such as those scrap materials resulting from the production, use and recycling of aluminum can bodies and ends preparatory to remelting the same in a metallurgical furnace.
As part of this scrap recycling process, aluminum can bodies and ends, after being collected, are cleaned, crushed and then shredded into small irregular fragments that normally range in particle size from about 1 to 11/2 inches. Prior to being remelted, these shredded aluminum particles are desirably first beneficiated, i.e., subjected to selected elevated temperatures to drive off the volatiles, such as the paints, lacquers and coatings that cover the particles. This beneficiation of the scrap materials by heating is effected primarily by vaporization of the volatiles associated with the scrap materials and the avoidance of ignition and burning of the volatiles inasmuch as ignition and burning of the volatiles can lead, among other things, to the ultimate burning and oxidizing of the metal rather than its beneficiation and recovery.
The avoidance of burning is important for another reason in that the conventional materials from which most or many of the aluminum can bodies and ends are presently made generally comprise aluminum alloy materials designated as a 3004 alloy by the Aluminum Association for the can bodies and 5182 and 5082 aluminum alloys for the can ends. The aluminum ends are normally double seamed to the can bodies and remain connected to the can bodies from the time the can bodies are filled with a beverage or beer, etc. and seamed until they are ultimately fully recycled and melted down. The 5000 series aluminum alloys contain magnesium as a major alloying ingredient while magnesium is present to some extent in the aforementioned 3000 series aluminum alloy. During heating and beneficiation of the scrap metal can ends and bodies containing magnesium, the possibilities of burning of the scrap can be aggravated due to the presence of the magnesium. When burning occurs a substantial amount of otherwise recoverable aluminum metal can become oxidized and lost. All of these factors detract from the desired maximum recovery of the aluminum metal material and the overall results of the recycling process.
The above-noted problems involved in the beneficiation of shredded aluminum scrap to obtain the maximum recovery of the aluminum for remelt purposes have not been satisfactorily solved by use of the procedures and equipment presently normally available for recovering and beneficiating scrap metal and the like, such as those represented, for example, by U.S. Pat. No. 1,869,886; 2,977,255; 3,116,545; 3,346,417; 3,322,529; 3,598,649; 3,650,830; 3,817,697; 3,821,026; 3,839,086 and Canadian Pat. No. 944,568.